add a way to selectively write to RefreshState

All resources use EvalWriteState to store their state, so we need a way
to switch the states when the resource is refreshing vs when it is
planning. (this will likely change once we factor out the EvalNode pattern)

terraform/eval_state.go

@@ -13,6 +13,13 @@ import (
 	"github.com/hashicorp/terraform/tfdiags"
 )
 
+type phaseState int
+
+const (
+	workingState phaseState = iota
+	refreshState
+)
+
 // EvalReadState is an EvalNode implementation that reads the
 // current object for a specific instance in the state.
 type EvalReadState struct {
@@ -220,6 +227,10 @@ type EvalWriteState struct {
 	// Dependencies are the inter-resource dependencies to be stored in the
 	// state.
 	Dependencies *[]addrs.ConfigResource
+
+	// targetState determines which context state we're writing to during plan.
+	// The default is the global working state.
+	targetState phaseState
 }
 
 func (n *EvalWriteState) Eval(ctx EvalContext) (interface{}, error) {
@@ -230,7 +241,15 @@ func (n *EvalWriteState) Eval(ctx EvalContext) (interface{}, error) {
 	}
 
 	absAddr := n.Addr.Absolute(ctx.Path())
-	state := ctx.State()
+
+	var state *states.SyncState
+	switch n.targetState {
+	case refreshState:
+		log.Printf("[TRACE] EvalWriteState: using RefreshState for %s", absAddr)
+		state = ctx.RefreshState()
+	default:
+		state = ctx.State()
+	}
 
 	if n.ProviderAddr.Provider.Type == "" {
 		return nil, fmt.Errorf("failed to write state for %s: missing provider type", absAddr)

terraform/node_resource_plan_instance.go

@@ -107,8 +107,8 @@ func (n *NodePlannableResourceInstance) evalTreeManagedResource(addr addrs.AbsRe
 	var provider providers.Interface
 	var providerSchema *ProviderSchema
 	var change *plans.ResourceInstanceChange
-	var refreshState *states.ResourceInstanceObject
+	var instanceRefreshState *states.ResourceInstanceObject
-	var planState *states.ResourceInstanceObject
+	var instancePlanState *states.ResourceInstanceObject
 
 	return &EvalSequence{
 		Nodes: []EvalNode{
@@ -129,10 +129,10 @@ func (n *NodePlannableResourceInstance) evalTreeManagedResource(addr addrs.AbsRe
 				Addr:           addr.Resource,
 				Provider:       &provider,
 				ProviderSchema: &providerSchema,
-				Output:         &refreshState,
+				Output:         &instanceRefreshState,
 			},
 			&EvalRefreshDependencies{
-				State:        &refreshState,
+				State:        &instanceRefreshState,
 				Dependencies: &n.Dependencies,
 			},
 			&EvalRefresh{
@@ -141,14 +141,15 @@ func (n *NodePlannableResourceInstance) evalTreeManagedResource(addr addrs.AbsRe
 				Provider:       &provider,
 				ProviderMetas:  n.ProviderMetas,
 				ProviderSchema: &providerSchema,
-				State:          &refreshState,
+				State:          &instanceRefreshState,
-				Output:         &refreshState,
+				Output:         &instanceRefreshState,
 			},
 			&EvalWriteState{
 				Addr:           addr.Resource,
 				ProviderAddr:   n.ResolvedProvider,
-				State:          &refreshState,
+				State:          &instanceRefreshState,
 				ProviderSchema: &providerSchema,
+				targetState:    refreshState,
 			},
 
 			// Plan the instance
@@ -160,9 +161,9 @@ func (n *NodePlannableResourceInstance) evalTreeManagedResource(addr addrs.AbsRe
 				ProviderAddr:        n.ResolvedProvider,
 				ProviderMetas:       n.ProviderMetas,
 				ProviderSchema:      &providerSchema,
-				State:               &refreshState,
+				State:               &instanceRefreshState,
 				OutputChange:        &change,
-				OutputState:         &planState,
+				OutputState:         &instancePlanState,
 			},
 			&EvalCheckPreventDestroy{
 				Addr:   addr.Resource,
@@ -172,7 +173,7 @@ func (n *NodePlannableResourceInstance) evalTreeManagedResource(addr addrs.AbsRe
 			&EvalWriteState{
 				Addr:           addr.Resource,
 				ProviderAddr:   n.ResolvedProvider,
-				State:          &planState,
+				State:          &instancePlanState,
 				ProviderSchema: &providerSchema,
 			},
 			&EvalWriteDiff{